<template>

  <ul class="list">
    <li class="item"
        v-for="key in indexs"
        :key="key"
        :ref="key"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleClick">
      {{key}}
    </li>
  </ul>
</template>
<script>
  export default {
    name: 'Alphabet',
    props: {
      cities: Object
    },
    data() {
      return {
        touchStatus: false,
        startY:0,
        timer:null
      }
    },
    updated(){
      this.startY=this.$refs['A'][0].offsetTop
    },
    computed: {
      indexs() {
        const indexs = []
        for (let i in this.cities) {
          indexs.push(i)
        }
        return indexs;
      }
    },
    methods: {
      handleClick(event) {
        this.$emit("change", event.target.innerText)
      },
      handleTouchStart() {
        this.touchStatus = true;
      },
      handleTouchMove(e) {
        if (this.touchStatus) {
          if(this.timer){
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY - this.startY) / 20)
            if (index >= 0 && index < this.indexs.length) {
              this.$emit("change", this.indexs[index])
            }
          },16)
        }
      },
      handleTouchEnd() {
        this.touchStatus = false;
      },
    }
  }
</script>
<style lang="stylus" scoped>
  @import "~styles/varibles.styl"
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    right 0
    top 1.58rem
    bottom 0
    width .4rem
    .item
      text-align center
      line-height .4rem
      color $bgColor
</style>
